Shunt excited log periodic antenna with coax feed



NOV. 28, 1967 I BELL ET AL 3,355,739

SHUNT EXCITED LOG PERIODIC ANTENNA WITH COAX FEED Filed Nov. 4, 1964 4 Sheets-Sheet l FIG I H INVENTORS R053 L. BELL ROBERT L. BARREL ORVILLE L. M CLELLAND av r v arm? NOV. 28, 1967 BELL ETAL I 3,355,739

SHUNT EXCITED LOG PERIODIC ANTENNA WITH COAX FEED Filed Nov. 1, 1964 4 Sheets-Sheet 2 .x 37a /34a /37a' 36a 370" 33 370" L k J; J

L I 1 1 1 1 H u 4/ 38 0 380" 4/' 4/ 3 J ,11/ 380 FIG 3 PRIOR ART 34b 37 36b 37b PRIOR ART INVENTORS R038 L. BELL ROBERT L. CARREL ORVILLE L. M CLELLAND TTO NEY Nov. 28, 1967 R BELL ET AL 3,355,739

SHUNT EXCITED LOG PERIODIC ANTENNA WITH COAX FEED Filed Nov/ 1, 1964 4 Sheets-Sheet 5 FIGS Rn N/ 4 RM ORVILLE L. MCCLELLAND BY I Z? ATTORNEYS Nov. 28, 1967 BELL ET AL 3,355,739

SHUNT EXCITED LOG PERIODIC ANTENNA WITH COAX FEED Filed Ndv. 4, 1964 4 Sheets-Sheet 4 45 FIG 7 FIG I20 E 240 I C O 10 I50 8 I80 6 LL] D. (D LU DC I 5 FIG |O m /,\'v[51\/"1'01 s 5 6 IO l4 I8 22 2s 30 54 555? 5555 FREQUENCY MC ORVILLE L. MCCLELLAND ATTORNEY United States Patent M 3,355,739 SHUNT EXCITED L9G PERIODIC ANTENNA Will-l CGAX FEED Ross L. Bell, Dallas, and Robert L. (Zarrei, Richardson, Tenn, and Orville L. Mcfiicllanil, (Zanoga Park, (Ialiti, assignors to Collins Radio Company, Cedar Rapids, liowa, a corporation of lawn Filed Nov. 4, we l, Ser. No. 408,781 8 Claims. (Cl. 343-7925) ABSTRACT OF THE DISCLOSURE A broadband log periodic type antenna array with a series of monopole elements alternately attached electrically and structurally to opopsite sides of a longeron and diverging from an apex with monopole elements increasing uniformly and proportionally with increasing distance from the apex. It includes two opposite side feeders connected to a common coaxial feed without utilizing a balun with each side feeder having series inductances and shunt capacitances and with coax shield sections spanning the Width of respective monopoles and in direct electrical contact with both forward and rear portions of the monopoles.

This invention relates in general to the feed of log periodic antenna structures, and in particular to a shunt excited coax feed for log periodic antennas.

Various log periodic antennas have been developed within the recent past having desirable properties in maintaining relatively constant radiation patterns and impedances over relatively large frequency bands in the order of 10:1 or even greater. Many of these antennas perform quite satisfactorily for many applications through some frequency ranges. However, many are found not to be particularly compatible for use with systems operating in high frequency ranges that require coaxial transmission lines as the interconnecting RF transmission line links between the antenna and other equipment such as transmitters and receivers without requiring the use of RF transforming baluns or other transformers. Use of coaxial transmission lines as interconnection RF cable links assumes critical importance where antennas must be steerable in azi muth and each imposes a requirement for a rotary joint. This is so since a variety of coaxial type rotary joints are readily available whereas RF slip ring assemblies having balanced transmission line characteristics and other suitable characteristics adequate to meet various design and performance requirements within suitable operational parameters are generally not available. Furthermore, the physical configuration of various prior art log periodic antennas present both structural and fabrication problems. Many of these earlier unidirectional log periodic antennas had two separate planar arrays of radiating elements diverging from the apex or feed point with repetitious antenna elements, the dimensions of which increase with increasing distance from the apex of the arrays. These structures occupy considerable volume with structural requirement problems magnified with operation in even moderate wind and/ or icing environments. Further, since these antennas must be excited in a balanced manner, they have generally used a balun transformer or a tapered line transformer applying the infinite balun technique for matching antenna impedance to the commonly used 50 ohm coaxial transmission lines. With such antenna structures, factors such as the use of an impedance matching device and the need for structural dielectric members for support of the two arrays of radiating elements electrically independent of each other, gave rise to functional and 3,355,739 Fatentetl Nov. 28, l7

structural problems that are readily apparent to those skilled in the art.

Further development have led more recently to planar types of log periodic antennas including such types as the log periodic dipole array, V array, tapered ladder array and also a shunt excited tapered ladder log periodic antenna. These planar type log periodic antennas obviously occupy less volume than the unidirectional two planar type log periodic antennas referred to above. However, although they have proven quite satisfactory in many ways, there are various limitations imposed by requirements for impedance transforming networks from 50 ohm coaxial transmission lines and the requirements for structural insulators to support the two arrays of radiating elements inherent in such planar log periodic antenna structures. While shunt excited log periodic planar antennas and tapered ladder antennas gave quite satisfactory operational radiation patterns and appropriate impedances, they still imposed a limitation in requiring balun transforming networks from 50 ohm coax transmission feed lines.

It is, therefore, a principal object of this invention to provide a log periodic type antenna of simple construction that can be coupled directly to a predetermined impedance value coaxial transmission line, for example, a 50 ohm coaxial transmission line, without the use of baluns or other transformer devices.

Another object is to provide such an antenna of relatively light weight, rugged construction capable of withstanding high winds and heavy ice loadings.

Another object is to provide a broadband log periodic antenna having a single longeron mounting monopole elements, in the form of fat monopole elements such as trapezoidal, triangular and conical elements or thin linear elements, longitudinally along the longeron and in alternate relation to opposite sides in an antenna structure capable of having an exceptionally wide frequency band and with the monopole elements being shunt excited.

A further object is to provide such a log periodic antenna having monopole elements mounted horizontally for horizontal polarization and attached electrically and structurally through connecting metallic members to a single common longeron which may be connected electrically and structurally to metallic masts or towers and rotators in turn connected to earth or a ground system for protection against lightning and the accumulation of static charges on the antenna.

Another object is to provide an antenna feed system with two feeder networks, a feeder network for elements on each side of a common longeron with each feeder network connected directly to the center conductor of the interconnecting coaxial transmission line for excitation, and with each of the two feeder networks comprised of low-pass transmission line components including both series inductances and shunt capacitances, and with each of these feeder networks connected to the common longeron in the region of the rear or large end of the log periodic antenna structure.

A further object of such a log periodic antenna is to provide lowpass feeder networks consisting of series in ductances and shunt capacitances utilizing straight lengths of conductors such as Wires, tubes, or rods for the series inductances and coax shields about portions of the wires, tubes, or rods as the shunt capacitors.

Still a further object is to provide such a log periodic antenna in which a low resistance D-C path is provided through each of the shunt feeder networks to permit operation of matrix switches and to provide for the use of test gear for insuring good connections in both the antenna and interconnecting RF coaxial transmission lines.

Features of this invention useful in accomplishing the above objects include, in a planar log periodic antenna,

a series of monopole elements that diverge from an apex and that connect electrically and structurally to a single longeron with the pertinent dimensions of the monopole elements increasing uniformly and proportionally with an increase in distance from the apex, and in which alternate monopole elements longitudinally spaced along a single common longeron are attached electrically and structurally to opposite sides of the longeron. It is a log periodic antenna having two opposite side feeder networks connected to a common coaxial feed without utilizing balun or other transformer devices. The feeder networks for the elements on each side of the common longeron connect directly to the center conductor of the interconnecting coaxial transmission line for excitation. Each of the feeder networks includes low-pass transmission line components, that is, series inductances and shunt capacitances and includes a feeder network connection to the common longeron at the rear or large end of the antenna structure. The series inductances are formed by straight lengths of conductors such as the wires, tubes, or rods that may be used in each of the feed networks, and the shunt capacitances are formed by coaxial shields about portions of the wires, tubes, or rods in providing the exciting shunt feed capacitive effect. It is a broadband log periodic antenna utilizing the phase rotation principle of asymmetrical log periodic antennas and the characteristics of low-pass transmission lines, with the proper phasing of currents being achieved in the elements in the active region and that through the region where the monopole elements are near resonance to permit efficient radiation. In a shunt excited log periodic antenna, utilizing applicants feed structure, energy from the antenna feed input terminals, when acting as a transmitter, travels along the two un balanced feeder networks towards the rear or large end of the antenna until it reaches the active region of the antenna, that region of the antenna where the monopole elements are near resonant length. From this location radiation occurs, since this is the active region of the antenna, to form a directional radiated beam in space in the direction toward the apex and toutward from the apex of the antenna.

A specific embodiment representing what is presently regarded as the best mode of carrying out the invention is illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 represents a perspective view of a prior art log periodic dipole array;

FIGURE 2, a partial schematic with one of two longerons cut away for a schematic showing of a tapered line transformer balun section;

FIGURE 3, a side view of a tapered ladder log periodic antenna including a balun and a two-wire line connection feed from the balun to the apex end of the antenna array and thereform to and through parallel shunt excitation sections symmetrically for both halves of each tapered ladder array section;

FIGURE 4, the partial top plan view of the tapered ladder log periodic antenna of FIGURE 3;

FIGURE 5, a perspective view of applicants novel shunt excited log periodic antenna with coax feed;

FIGURE 6, a partial top plan schematic view of the shunt excited log periodic antenna of FIGURE 5;

FIGURE 7, an enlarged fragmentary bottom view of the low-pass apex end feeding portion of the antenna of FIG- URES 5 and 6;

FIGURE 8, an enlarged fragmentary top view of a feeder section termination in the antenna of FIGURES 5 and 6;

FIGURE 9, typical E-plane and H-plane patterns obtained with the antenna; and

FIGURE 10, a plot of voltage standing wave ratio (VSWR) vs. frequency for one of applicants shunt excited log periodic antennas with coax feed with a 50 ohm coax transmission line feed input to the antenna.

Referring to the drawings:

The prior art planar antenna of FIGURES l and 2 is of the log periodic dipole type having two asymmetrical planar dipole array assemblies 21 and 22 that are series excited by a balanced feeder network formed with the planar dipole array assemblies 21 and 22 being electrically insulated and spaced from each other by dielectric structural members 23a, 23b, and 230. This feed system also requires an impedance transforming network 24 for matching antenna impedance to, for example, a 50 ohm coax RF transmission antenna feed line 25. The impedance transforming network 24 is a tapered line transformer extension from the center conductor of the coax line 25 through the input support dielectric member 26, and with the outer sheath of the coax cable directly electrically connected to planar dipole array assembly 21 at the input member 26 end. The other end of the tapered line transformer is passed through dielectric insulating end support member 27 and electrically connected to the apex end 28 of planar dipole array assembly 22. The antenna also requires an insulator 29 between the tower 30 and the lower planar dipole array assembly 21. While radiation patterns and the feed impedance match of such antennas are generally quite satisfactory, their usefulness is limited, for steerable beam requirements. This is particularly so with the extensive and heavy structural requirements imposed, with the additional expense imposed by the requirement for dielectric structural members 23a, 23b, and 230, and the like, and with the added expense of such impedance matching devices as the tapered line transformer 24.

Please refer also to FIGURES 3 and 4 for a prior art tapered ladder log periodic type antenna 31 mounted for rotation on a tower 32 as driven by a rotator. With this antenna structure a coax transmission line is passed up through the tower assembly 32 to a balun transformer 33 mounted on the antenna structure 31. This balun transformer 33 has two parallel output lines 34a and 3412 connected through antenna apex feed terminal mounting dielectric bracket 35 to the antenna apex input feed terminals. Antenna shunt excitation input leads 36a and 36b extend rearwardly from the apex end of the antenna from input terminal connections, respectively, with lines 34a and 34b rearwardly to the large end of the antenna. At each tapered ladder section of the log periodic antenna, the leads 36a and 36b pass through dielectric holders 37a and 37b at the opposite sides respectively, and successively, respectively through like holders 37a and 37a" of one side and on the other side 37b and 37b", and in like manner on through to the large end of the antenna. Each of the dielectric support members 37a and 37b, 37a, 37a, 37b, 37b, etc., also support a short stub line 38a and 38b, and successively 38a, 38a", 38b and 3812, etc., respectively, in inductive shunt excitation relation to respective portions of the lines 36a and 36b. Each of these shunt inductively excited stub lines 38a and 38b, etc., are terminated in an electrical connection on the forward and rear elements 3d and 40, 39 and 40, etc., respectively, of each tapered ladder section 41, 41, etc., at the respective opposite sides of each tapered ladder section.

While radiation patterns and the feed impedance match of the symmetrical log periodic array of the dipole elements in the tapered ladder log periodic antenna shown in FIGURES 3 and 4 as shunt excited through lines 36a and 36b and the short stub lines 38a and 38b, 38a, 38a", 38b, and 381)", etc., have been generally quite satisfactory, the usefulness of such antennas for steerable beam applications is limited in practice and costs are excessively high with the additional equipment required. Such expensive additional equipment includes the balun transformer equipment 33 as part of a complex feed system also requiring mechanical rotatable joints and coax line rotatable joint connections and a massive tower support 7 ing structure.

Please refer now to applicants shunt excited log periodic antenna 42 with coax feed, as shown generally in FIGURE 5, and with various details illustrated by FIG- URES 6, 7, and 8. The antenna 42 is shown to consist of a planar array 43 of triangular shaped monopole elements 44a and 44b, and 44a and 44a", and, 44b and 44!)" extending successively and alternately from the apex end in geometrically increasing size from the apex feed T connection 45 equipped end of the planar array 43. The planar array 43 includes an electrically conductive boom longeron 46 with the triangular shaped monopole elements 44 carrying the a designation fastened structurally and electrically on one side of the boom longeron and those carrying the 44 b designation fastened structurally and electrically to the other side. The boom longeron 46 is fixed to the top bracket 47 of a rotatable tube mast 48 which in turn is supported by a base antenna rotary drive unit 49 positioned on the ground, and with this structure providing an electrical conductive path through the antenna mast between the boom longeron 46 and ground through the rotary drive unit. A coaxial transmission line 50 extends from connections with RF transmitting and possibly receiving equipment (not shown) to the base antenna rotary drive unit 49. A portion 54) of the coaxial cable transmission line extends from the drive unit 49 through an opening 51 to the interior of the tubular mast dd with suflicient slack to pertmit 180 rotation of the mast and antenna in both directions from a center position. The line t? extends from the opening 51 vertically upward through the tubular mast 48 to an outlet opening 52 and has an external portion 50', extending to opening 53 in boom longeron 46, with sufficient slack to permit articulation of the planar array 43 relative to the mast 48 as the antenna is being raised or lowered. From the entrance opening 53 of boom longeron 46, coaxial line 50 extends forward within the tubular longeron 46 to a planar array 43 apex end mounting dielectric assembly 54 and the coax center line 55 output apex feed T connection 45 for the planar array 43.

The antenna feed for planar array 43 includes two opposite side feeder lines 56a and 56b extending from the apex feed T connection 45 to substantially the rear of the antenna planar array 43. At each of the respective monopole elements 44a and 44b and the successive primed monopole elements, the lines 55:: and 56!) are passed through respective coaxial shunt excitable shield sections 57a and 57b and successively and alternately 57a and 57a", and 57b and 5711, etc., from the apex end with each coaxial shunt excitable shield section having successively increasingly greater capacitive value from the apex location alternately according to the following order: 57a, 57b, 57a, 57b, 57a", 7b, etc. Each coaxial shunt excitable shield section 57a and 57b and the successive primed sections are structurally mounted and connected electrically to the respective monopole elements Ma and 44b and the successive primed units with the respective coaxial shunt excitable shield sections spanning substantially the base of the respective monopole elements.

Please note that as the monopoles increase in size with distance from the apex of the planar array 43 and with the successively larger coaxial shunt excitable shield sections, their spacing increases from a narrow spacing relative to the respective sides of the longeron in at the apex end geometrically progressively to considerably more substantial spacing at the large end of the planar array 43. Further, the sections of lines 56a and 5611 between adjacent coaxial shunt excitable shield sections increases both in length and in spacing from the respective sides of the longeron 46 progressively from front to rear. The feeder lines 56a and 56b form series inductor lengths extending to shunt capacitor sections with the series inductor lengths and the continued feed line through shunt capacitors being constructed of a simple linear metallic conductor. Further, the shunt capacitor sections 57a and 57b, etc., are constructed of metallic tubes coaxial with and extending over portions of the respective feeder lines 56a and 56b but are not in physical contact with the respective feeder lines except through intervening dielectric insulating material spacers or the like.

Commercially available lumped capacitors in various sizes could be used as shunt capacitors connected between the feeder lines 56a and 56b and suitably located tap connections on the respective monopole elements 44a and 44b, and the like, in place of various, or all of the coaxial shunt excitable shield sections 57a and 57b and the like. This could be provided in an antenna feed structure with inductances and capacitance values adjusted to provide the desired impedance level and giving substantially the same performance as provided with applicants antenna using only coaxial shunt excitable shield sections in the feed networks.

Various antennas according to appiicants teaching can provide desired operation results with unterminated feeder line stubs at the large end of the antenna array 43. However, applicants in various antenna embodiments, in order to minimize antenna size, provide terminating elements such as inductor coils 58a and 58b connected between the rear end of the respective feeder lines 56a and 56b and electrical connection with the respective sides of longeron 46 as illustrated in FIGURES 6 and 8.

During operation the monopole elements that increase in size and spacings and extend alternately to opposite sides with increase in distance from the apex of the antenna array 43, are shunt excited from the unbalanced low-pass feeder system. This is accomplished with the opposite side feeder lines 56a and 5612 being used to excite mon-opoles on respective sides of the longeron, particularly with these side feeding network systems including operational series inductance and shunt capacitance combinations. Energy supplied from coax transmission line 5th through T connection 45 when the antenna is used as a transmitter, travels along the two low-pass feeder lines 56a and 56b until it reaches an active region of the antenna on one side or the other of the antenna planar array 43 with that active location being the region where the respective monopole element or elements are near resonant length. At this active region location, energy is actively coupled from the feeder line network into the respective monopole element or elements and radiated into free space. The radiated lobe consists of a unidirectional beam originating from the active region and directed toward and through the apex of the antenna planar array 4-3.

Referring particularly to FIGURE 6, the angle a is the angle formed by the line extending through the extremities of the monopole elements, X is an element length measurement, R, an element distance from the apex measurement with appropriate subscripts of n-1, n, n+1, etc., being utilized to denote the respective distances and measurements relative to the various radiating monopole elements. The pertinent substantially coplanar dimensions R and X pertaining to the various individual elements difiier only from the corresponding values with respect to adjacent elements only by a scale factor 1', so that, for example:

The parameter 'r is constant for a given antenna and has a value of less than unity. The frequency range over which the antenna will operate is determined by the size of antenna, i.e., the number of mono-poles, with the longest monopole being of resonant length at a frequency which is slightly lower than the lowest operating frequency and the shortest element being resonant at a frequency slightly higher than the upper operating frequency.

'2 The values of the series inductances L and shunt capacitances C vary proportionally with the change in lengths of the monopoles by the constant 1', or

Thus, values L and C are directly proportional to the size of the monopole elements. Feeder lines appear as constant impedance RF lines between the antenna terminals and the active region and the characteristic impedance Z of the feeder lines is approximated by the equation where L is the series inductance in henries and C is the shunt capacitance in farads. Since the ratios of the values of L and C are constant for all monopoles, Z is constant for all frequencies below some cutolf frequency fc. Cutoff or resonance occurs when the magnitude of the positive series reactance is equal to the magnitude of the negative shunt reactance. The cutoff frequency fc is approximated by:

Hence, the cutoff frequency of the sections of the lowpass feeder network varies in the same manner as the resonant frequencies of the monopoles, i.e., the short monopoles are resonant at high frequencies and corre sponding feeders have high cutoff frequencies, and long monopoles have low resonant frequencies and corresponding feeders have low cutoff frequencies. It is important for proper operation, that the cutoff frequency of the feeder section be approximately the same as the resonant frequency of the monopole element.

While this antenna is described primarily with respect to operation in the transmission mode, it is a dual transmit-receive antenna also useful for the receive mode of operation. However it might be noted that material problems in a transmit mode of operation are not generally problems of such magnitude in the receive mode of operation. In any event, in the transmit mode of operation radiated RF signal energy to be transmitted travels from the planar array apex terminal to the active region of the antenna corresponding to the operating frequency. The feeder lines and coax shield sections between the antenna terminal and the active region appear essentially as a constant impedance RF transmission line. In the active region the positive reactances of the inductances and the negative reactances of the capacitors tend to cancel thereby coupling energy directly into the monopoles at the connection points between the respective shield capacitive sections 57a and 57b with the respective monopole or monopoles and RF radiation occurs in the transmit mode. This develops a radiating RF energy lobe in the form of a unidirectional beam directed toward and outward through the apex of the planar antenna array 43.

The antenna may be thought of as supporting two RF waves with the first being a transmission line wave which couples energy to the monopole elements and the second being a radiated wave from the active region. The transmission line wave travels from the apex feed terminal toward the large end of the planar antenna array structure and the resulting radiated wave travels back from the activated region toward the apex of the planar antenna array structure. The reversal of direction between these two RF waves is brought about in the following manner. Signal currents of the transmission line RF Wave of each successive longer monopole lags that of the previous monopole by approximately 90 in the active region. These currents produce radiation, however, by virtue of the 180 space phasing between alternate mono- 8 poles; that is, with the alternate monopoles extending in opposite directions to opposite sides from the longeron with the radiation current of each successively shorter monopole lagging that of the previous monopole by approximately to thereby direct RF radiation from the activated region toward the smaller elements and apex of the antenna array in the radiated RF signal wave lobe.

Obviously, various design parameter combinations will provide satisfactory operation results. For example, using 7:0.841, oz=60 and with two X dimensions, of the various X dimension values, being 41 feet and 6 feet, an antenna is provided with broadband operation through the range from 6.5 to 30 me.

The resulting advantageously optimized radiation E and H patterns are illustrated in FIGURE 9 and a plot of V SWR with respect to 50 ohms to frequency in FIGURE 10 shows a very advantageously low VSWR range of variation throughout an extensively broad range of frequencies.

Whereas this invention is here illustrated and described with respect to a specific embodiment thereof, it should be realized that various changes may be made without departing from the essential contribution to the art made by the teachings hereof.

We claim:

1. A broadband antenna planar array structure having a common longitudinally extended center portion, a forward apex feed end, and an enlarged back end; monopole elements longitudinally spaced along said center portion and extending outwardly therefrom in planar relation and in opposite directions alternately from the forward apex feed end to the enlarged end of the antenna planar array structure, and with substantially coplanar dimensions and spacings of the monopole elements increasing uniformly and proportionally with increase in distance from the apex feed end of the antenna planar array structure; said antenna planar array structure being provided with a connection to a coaxial transmission line having an outer sheath and an inner conductor line; two feeder network lines for feeding the monopole elements of each side of said planar array structure; said connection to a coaxial transmission line including common connective means for the two feeder network lines and the inner conductor of the coaxial transmission line at the forward apex feed end of the antenna planar array structure; and capacitive means connected between the respective feeder lines of the feeder networks and the respective monopoles of the planar array structure wherein said monopole elements are fat monopole elements with substantially coplanar dimensions of the monopole elements increasing uniformly and proportionally with an increase in distance from the forward apex feed end of the antenna planar array structure; the capacitive means connected between the respective feeder lines of the feeder networks and the respective fat monopole elements of the planar array structure includes respective portions of conductor length and coax shield formed shunt capacitors; each of said fat monopole elements has a forward portion and a rear portion; with the respective shunt capacitive coax shields structurally mounted on and in electrical contact with the respective fat monopoles; and wherein the coax shield of the capacitive means connected to each respective fat monopole element spans the fat monopole from said forward portion to said rear ward portion and is in direct electrical contact with both said forward and rear portions of the respective fat monopole element.

2. The broadband antenna planar array structure of claim 1, wherein the fat monopole elements are triangular monopole elements.

3. The broadband antenna planar array structure of claim 1, wherein each said shunt capacitor is successively of increasingly greater capacitive value from the apex location in alternate relation toward the enlarged back end of the antenna planar array structure, and with successively larger value shunt capacitors provided with successively increased spacing from the electrical conductive means interconnecting the monopole elements.

4. The broadband antenna planar array structure of claim 3, wherein sections of the two feeder network lines between the coax shields of respective shunt capacitors increase both in length and in spacing from the respective sides of said electrical conductive means interconnecting the monopole elements progressively from the forward apex feed end to substantially the enlarged back end of the antenna planar array structure.

5. The broadband antenna planar array structure of claim 1, wherein electrical conductive means interconnects said monopole elements in the region of said common longitudinally extended center portion the common longitudinally extended center portion is longeron structure extending from the forward apex feed end to the enlarged back end of the antenna planar array structure; said lon-geron structure is a single hollow longeron of conductive material to which the monopole elements are connected both electrically and structurally; said planar array structure is mounted on an antenna mast and wherein said coaxial transmission line, having an outer sheath and an inner conductor line, extends up the mast and into the interior of said single hollow longeron at a location adjacent the antenna mast; and with the coaxial transmission line extending forward within said single hollow longeron to the apex feed end of the antenna planar array structure; and wherein said antenna mast it) provides an electrical conductive path between the couductive material forming said hollow longeron and ground.

6. The broadband antenna planar array structure of claim 2., wherein the outer sheath of said coaxial transmission line is electrically connected to the conductive material forming said single hollow longeron.

7. The broadband antenna planar array structure of claim 5, wherein each of said two feeder network lines for feeding the monopole elements on each side of said planar array structure are each provided with an electrical conductive connection with said electrical conductive means interconnecting said monopole elements substantially at the enlarged back end of the antenna planar array structure.

8. The broadband antenna planar array structure of claim 7, wherein each electrical conductive connection between the two feeder network lines and said electrical conductive means includes inductive coil means.

References Cited UNITED STATES PATENTS 3,134,979 5/1964 Bell 343-792.5 3,193,831 7/1965 Yang 343--792.5 3,276,027 9/1966 Bell et al 343--792.5

HERMAN KARL SAALBACH, Primary Examiner.

PAUL GENSLER, Examiner. 

1. A BROADBAND ANTENNA PLANAR ARRAY STRUCTURE HAVING A COMMON LONGITUDINALLY EXTENDED CENTER PORTION, A FORWARD APEX FEED END, AND A ENLARGED BACK END; MONOPOLE ELEMENTS LONGITUDINALLY SPACED ALONG SAID CENTER PORTION AND EXTENDING OUTWARDLY THEREFROM IN PLANAR RELATION AND IN OPPOSITE DIRECTIONS ALTERNATELY FROM THE FORWARD APEX FEED END TO THE ENLARGED END OF THE ANTENNA PLANAR ARRAY STRUCTURE, AND WITH SUBSTANTIALLY COPLANAR DIMENSIONS AND SPACINGS OF THE MONOPLE ELEMENTS INCREASING UNIFORMLY AND PROPORTIONALLY WITH INCREASE IN DISTANCE FROM THE APEX FEED END OF THE ANTENNA PLANAR ARRAY STRUCTURE; SAID ANTENNA PLANAR ARRAY STRUCTURE BEING PROVIDED WITH A CONNECTION TO A COAXIAL TRANSMISSION LINE HAVING AN OUTER SHEET AND AN INNER CONDUCTOR LINE; TWO FEEDER NETWORK LINES FOR FEEDING THE MONOPOLE ELEMENTS OF EACH SIDE OF SAID PLANAR ARRAY STRUCTURE; SAID CONNECTION TO A COAXIAL TRANSMISSION LINE INCLUDING COMMON CONNECTIVE MEANS FOR THE TWO FEEDER NETWORK LINES AND THE INNER CONDUCTOR OF THE COAXIAL TRANSMISSION LINE AT THE FORWARD APEX FEED END OF THE ANTENNA PLANAR ARRAY STRUCTURE; AND CAPACITIVE MEANS CONNECTED BETWEEN THE RESPECTIVE FEEDER LINES OF THE FEEDER NETWORKS AND THE RESPECTIVE MONOPOLES OF THE PLANAR ARRAY STRUCTURE WHEREIN SAID MONOPOLE ELEMENTS ARE FAT MONOPOLE ELEMENTS WITH SUBSTANTIALLY COPLANAR DIMENSIONS OF THE MONOPOLE ELEMENTS INCREASING UNIFORMLY AND PROPORTIONALLY WITH AN INCREASE IN DISTANCE FROM THE FORWARD APEX FEED END OF THE ANTENNA PLANAR ARRAY STRUCTURE; THE CAPACTIVE MEANS CONNECTED BETWEEN THE RESPECTIVE FEEDER LINES OF THE FEEDER NETWORKS AND THE RESPECTIVE FAT MONOPOLE ELEMENTS OF THE PLANAR ARRAY STRUCTURE INCLUDES RESPECTIVE PORTIONS OF CONDUCTOR LENGTH AND COAX SHIELD FORMED SHUNT CAPACITORS; EACH OF SAID FAT MONOPOLE ELEMENTS HAS A FORWARD PORTION AND A REAR PORTION; WITH THE RESPECTIVE SHUNT CAPACITIVE COAX SHIELDS STRUCTURALLY MOUNTED ON AND IN ELECTRICAL CONTACT WITH THE RESPECTIVE FAT MONOPOLES; AND WHEREIN THE COAX SHIELD OF THE CAPACITIVE MEANS CONNECTED TO EACH RESPECTIVE FAT MONOPOLE ELEMENT SPANS THE FAT MONOPOLE FROM SAID FORWARD PORTION TO SAID REARWARD PORTION AND IS IN DIRECT ELECTRICAL CONTACT WITH BOTH SAID FORWARD AND REAR PORTIONS OF THE RESPECTIVE FAT MONOPOLE ELEMENT. 